Technical Abstract:
There is growing interest in strategies to improve the nutritional quality of our food supply, especially with respect to essential micronutrient minerals, such as iron and zinc, and the pro-vitamin A carotenoid, beta-carotene. Recent estimates indicate that one-third of the world’s populations are at risk for iron-deficiency-induced anemia, a condition considered to be the most prevalent nutrient-related human disease on the planet. An almost similar proportion of individuals may be zinc deficient, and as many as 250 million children are estimated to be at risk for vitamin A deficiency. The primary reason for these problems is that most individuals, especially in developing countries, consume diets composed mainly of plant foods, and these plant foods are generally low in Fe and Zn concentrations (relative to animal-derived foods). Furthermore, the bioavailability of these minerals in plant foods is generally low. Similarly, when discussing staple food crops, beta-carotene concentration can be low to nonexistent. Thus, we and others have been attempting to develop approaches that would facilitate significant increases in the micronutrient content, and/or bioavailability, of plant foods; we are particularly interested in improving the nutritional value of staple crops such as rice, wheat, maize, bean, cassava, and sweet potato, as this would have the most significant nutritional impact on at-risk human populations. In this talk, we will discuss recent efforts to improve micronutrient concentrations in plant foods, as well as efforts to quantify and understand micronutrient bioavailability. For the cases of Fe and Zn, our scientific approach has been to identify and characterize the underlying mechanisms and regulatory components that are responsible for whole-plant metal homeostasis. Because iron and/or Zn acquisition appears to be homeostatically regulated in order to ensure adequate (but not excess) metal nutrition, the integration of these homeostatic mechanisms is ultimately responsible for determining Fe and Zn content in edible organs. Thus, we believe that by identifying the rate-limiting mechanisms at the root-soil interface, at the boundary of various compartments within roots, at the point of phloem loading in leaves, etc., we should be able to determine what steps must be taken to effectively manipulate micronutrient mineral levels within plants. We will present working models of whole-plant metal homeostasis, and will review our current understanding of the identified components and control points in these models. With respect to bioavailability issues, we will discuss recent studies with Golden Rice, the transgenic plant that produces beta-carotene in the grain endosperm. We have been studying beta-carotene bioavailability using a stable isotope approach, and have been attempting to identify food components that influence Fe and Zn bioavailability using a quantitative genetics approach. Progress in these areas will be presented.